1. Technical Field
The present invention relates to antenna systems and, more particularly, to adaptive control of an antenna system particularly applicable for use in receiving digital RF signals for digital television (DTV).
2. Description of the Prior Art
In the United States, the Federal Communications Commission (FCC) has established guidelines for broadcasting television signals. The established standard is known as the NTSC signal format which is an analog signal. The FCC is now permitting the broadcasting of digital television (DTV) as well as analog NTSC signals.
The digital television signals (DTV) being broadcast at this time are horizontally polarized signals. Circular polarized signals (CP) are being considered for future broadcasting of digital television signals. A problem noted with such horizontally polarized DTV signals arises in urban centers having tall buildings. The DTV signal may reflect off one or more buildings prior to being received at a subscriber""s receiving antenna. If the receiving antenna is a xe2x80x9crabbit earxe2x80x9d di-pole antenna, the received signal may be comprised of the horizontal component (from the broadcasted horizontally polarized DTV signal) as well as a vertical component (the result of reflection). The reflected vertical component may lead or lag the horizontal component in time and be offset therefrom in phase, resulting in an erroneous xe2x80x9cghostingxe2x80x9d signal being fed to the subscriber""s DTV television receiver. The result will be a garbled picture on the television receiver.
It is understood that the same result will take place if the broadcasted signal is circularly polarized (CP). Such a signal, when received at a receiving antenna, will include a horizontal component and a vertical component together with a vertical reflection component and a horizontal reflection component resulting in erroneous signals being fed to the DTV television receiver.
An antenna system for receiving horizontal and vertical components of a transmitted horizontally polarized digital RF signal. The system includes a vertical antenna for primarily receiving vertical components of the RF signal and a horizontal antenna primarily for receiving the horizontal components of the RF signal. An adjustable time delay adjuster is provided for adjusting any time delay of one of the components. A combiner combines the components to obtain therefrom a combined RF signal for application to an RF utilization means. The combined RF signal is a digital signal exhibiting a bit error rate dependent upon the value of the vertical component. An RF decoder decodes the bit error rate and provides a bit error rate signal having a value that varies as a function of the value of the bit error rate. An adaptive controller responds to the bit error rate signal and adjusts the time delay adjuster in a direction to decrease the value of the bit error rate signal.